A long-standing problem associated with the use of heat pumps in most parts of the world is that frequently the outdoor coil will, during the heating mode of operating, have frost/ice accumulate and built-up thereon. As the ice thickness increases, the overall efficiency of the heat pump system decreases significantly, and a substantial amount of energy may be wasted. Accordingly, many arrangements have been proposed heretofore for detecting the frost and/or ice and for taking corrective action for removing the frost/ice from the outdoor coil. Examples of prior art systems include the following U.S. Pat. Nos.: 3,170,304; 3,170,305; 3,400,553 and 4,2090,994.
It has been recognized that, for a given set of criteria, there is an optimum point (of frost/ice build up) at which to command a defrost mode of operation of the heat pump system. If defrost is commanded too soon or too late, energy will be wasted, i.e., total system efficiency will suffer.
The present invention is an adaptive defrost control system which is self-adaptive so that for each cycle of operation of the heat pump system, i.e., a heating operation followed by a defrost mode of operation followed by another heating cycle, etc. there will be a modification of the control apparatus so as to readjust the control point for initiating defrost.